Damping network



Oct. 21, 1969 Filed 001:. 5, 1966 2 Sheets-Sheet 1 I I4 27 F 2 Wolfgang Hoffmann Se\ector Position 10 a0 so so so Friedrich Neusch'eler (21)10db X X x X Eberhard Schuon Pudsin 21' zo X X X X INVENTORS. cimui" (21")3Udb x x x x (21"')30db x x x x x Oct. 21, 1969 w, gF ET AL 3,474,356

DAMPING NETWORK 2 Sheets-Sheet 2 Filed Oct.

I as

gang Hoffmann Friedrich Neuscheler Eberhard Schuon l.\'\ '15 \"IURS.

United States Patent US. Cl. 333-81 Claims Our present invention relates to a damping network of the type wherein several attenuation pads are selectively connectable in cascade in a circuit for the transmission of signal waves, with maintenance of the continuity of the circuit irrespectively of the number of attenuation pads operatively connected therein. Such networks are widely used in communication systems for purposes of calibration or for the actual insertion of a desired amount of damping in a transmission line.

The general object of this invention is to provide a damping network of the character described which can be used over a broad band of signal frequencies for the selection of different damping factors.

A more particular object of this invention is to provide a mounting for the elements of such a damping network which avoids the introduction of stray fields or parasitic reactances upon the insertion or disconnection of any attenuation pad, thereby insuring the maintenance of a given phase constant or wave impedance under all operative conditions.

These objects are realized, pursuant to our present invention, by the provision of a support for each attenuation pad on which the impedance elements, one or more switching relays for the selective insertion or disconnection thereof, and a control circuit for the actuation of such relay or relays are mounted, the supports of the several pads being provided with coupling means, such as plugs and jacks, for electrical interconnection with the other pads and being physically separated from a selector unit which is common to the several control circuits for individually actuating their relays. The operation of the selector unit, therefore, is without influence upon the passive impedance elements of the several pads and has no effect other than the switching of these elements into and out of circuit by the energization or deenergization of the associated relays.

In a particularly compact arrangement, lacking all outwardly projecting switching devices, the support for each attenuation pad comprises a prismatic block formed with substantially cylindrical bores for the major impedance elements and with separate chambers for the relays, the latter being advantageously. in the form of magnetic reed switches of the general type known, for example, from US. Patent No. 3,059,075. We prefer to use a set of three reed relays per pad, two of these relays having their contact pairs in series with the impedance elements of the pad while the third relay has its contact pair connected across the series combination of these impedance elements with the two first-mentioned contact pairs. Thus, when the first two pairs of contacts are closed and the third pair is open, the pad is effectively connected in circuit between associated input and output terminals; when the contacts are reversed, the pad is disconnected at both ends and the third pair of contacts closes a direct path between the input and output terminals of the circuit. The choice of this type of relay switch is especially desirable because the capacitances of the open switch con- 3,474,356 Patented Oct. 21, 1969 tacts are well determined and may, therefore, be taken into account in the design of the pad so that its wave impedance is substantially independent of the state of energization of the relays. This will avoid undesirable variations of attenuation with frequency, cross-talk, and reflections.

The individual mounting blocks for the several attenuation pads of our improved damping network can be stacked together with the aid of suitable fastening means, the number of blocks in a stack being readily variable in accordance with requirements. This building-block principle thus affords a great deal of flexibility and adaptability to our system.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a circuit diagram of an attenuation pad forming part of a damping network according to the invention;

FIG. 2 is a switching diagram for our improved damping network, including a plurality of pads each of the type shown in FIG. 1;

FIG. 3 is a table used to explain the operation of the system of FIG. 2;

FIG. 4 is a front-elevational view, partly in section, of a mounting block supporting the elements of the pad illustrated diagrammatically in FIG. 1;

FIG. 5 is a top view (parts broken away) of the block of FIG. 4; and

FIG. 6 is a cross-sectional view of a reed relay forming part of the assembly of FIGS. 4 and 5.

In FIG. 1 we have shown an attenuation pad generally designated 21, having a pair of input terminals 4, 5 and a pair of output terminals 6, 7 between which a fourterminal network of T-type, composed of two series resistors 1, 2 and a shunt resistor 3, is connected in series with contacts 8,9 of two relays 11 and 12. Other impedances, optionally provided, include a pair of series inductances 58a and 58b, a shunt inductance 61 in series with resistor 3 and a shunt capacitance 60. The network is bridged by a line including two other optional inductances 58c, 58d in series with contacts 10 of a third relay 15.

A transistor 17, here shown to be of the NPN type, has its base collector circuit connected in parallel with the windings of relays 11, 12 between a control lead 14 and a positive bus bar extending from a terminal 13 of a direct-current source; the negative terminal 16 of that source is connected via another bus bar, through the winding of relay 15, to the emitter of transistor 17. A switch 24, forming part of a selector more fully described hereinafter with reference to FIG. 2, is operable to leave the control lead floating or to connect it to negative potential on terminal 16. In the former case, the base of transistor 17 is connected to positive potential through the windings of relays 11 and 12 so that the transistor conducts and energizes the relay 15, the base current being insuflicient to operate relays 11 and 12 whereby contacts 8 and 9 are open and contacts 10 are closed; terminals 4, 5 are then practically directly connected to terminals 6 and 7, except for the presence of the small inductances 58c, 58d and a slight capacitive coupling through the open contact pairs 8 and 9 in series with impedance elements 1, 2 and 58a, 5811. When the switch 24 is closed, which is the position illustrated in FIG. 1, the transistor 17 is cut oft and the windings of relays 11, 12 are connected directly across the terminal 13 and 16, thus closing contacts 8 and 9 while contacts 10 are opened by the release of relay 15.

The effect of the open-circuit capacitances of contacts 8, 9 and contacts 10, in one or the other switching position, is to reduce the wave impedance of the path 21 which, therefore, should exceed the desired magnitude in the absence of these capacitances. The series inductances 58a, 58b and 58c, 58d are designed to balance any overcompensation of the wave impedance by the capacitances of the relay contacts. Shunt inductance 61 is designed to compensate any increase in attenuation which may occur at high frequencies, particularly with networks of low damping factor, because of the skin effect. Shunt capacitance v60 has the purpose of compensating a reduction in attenuation which may occur at high frequencies, particularly with networks of high damping factor, by reason of the shunt capacitance of the open contacts 10. The physical realization of these various passive elements will be described hereinafter with reference to FIGS. 4 and 5.

In FIG. 2 we have diagrammatically illustrated the overall structure of our improved damping network, comprising two principal units 19 and 20 which are physically separated from each other and are electrically interconnected by plug-in couplings 18, 118 and 218. Unit 19 comprises several (here three) dec-adic groups of attenuation pads similar to the one shown in FIG. 1, i.e., a first group of pads 21, 21, 21", 21, a second group of pads 22, 22, 22", 22" and a third group of pads 23, 23', 23", 23'. The pads of each group are serially interconnected and the groups themselves .are connected in cascade between two terminals of a high-frequency source HF. The control leads of conductors 21, 21, 21" and 21" have been respectively designated 14, 14', 14", 14" and are extended via connectors 18 to a diode matrix 28 leading to or terminating at bank contacts No. 2 to No. 10 of an associated selector switch 24 whose No. 1 bank contact is left unconnected. In an analogous manner, control leads 114 and 214 extend from groups 22 etc. and 23 etc. via connectors 118 and 218 to diode matrices 128 and 228 terminating the bank contacts of decadic selector switches 25 and 26. The wipers of switches 24, 25'and 26 are connected to the negative pole 16 of the associated D-C source which has been designated 27 and forms part of unit 20.

The four attenuation pads of each group have damping factors which, in different combinations, yield ten decadic values of overall attenuation including the value in the first position of the associated selector switch in which none of the pads is connected in circuit. In the specific example illustrated, the damping factors have the ratio of l:2:3:3 though other ratios (e.g., 1:2:314 or 1:2:4:6) could also be chosen for yielding all the integral values from 1 to 9. More particularly, pads 21, 21', 21" and 21" are assumed to have damping factors of 10, 20, 30 and 40 db, respectively; the corresponding damping factors of groups 22 etc. and 23 etc. may have the same damping factors multiplied by a factor of 10 and a factor of 100, respectively. In this way, any one of a thousand different values of overall attenuation may be selected by the setting of the three decadic selector switches 24, 25 and 26.

The diode matrix 28, which is also representative of matrices 128 and 228, is so designed that energization of any of bank contacts No. 2 through No. 10 of switch 24 will connect the pads 21, 21, 21", 21" in circuit in the different combinations given in the table of FIG. 3, thus resulting in nine different values of attenuation ranging from 10 db to 90 db.

Reference will now be made to FIGS. 4-6 for a description of the physical construction of the pad 21 which is representative of all the attenuation pads diagrammatically indicated in FIG. 2. A prismatic block 29 of a metal of preferably low magnetic permeability, such as aluminum, is formed with several transverse bores 30 for the passage of connecting bolts, not shown, by which this block may be mechanically connected with other blocks, such as block-29' (FIG. supporting the pad 21 of FIG. 2, to form a stack. Block 29 also has complementary electric connections such as a plug 31 and a jack 32 mating with their opposite numbers on adjacent blocks;

since the electrical circuit shown in FIG, 1 is symmetrical, it is immaterial whether connections 31 and 32 respectively correspond to input terminal 4 and output terminal 6 (FIG. 1) or vice versa. The other two terminals 5 and 7 shown in FIG. .1 are at ground potential and are therefore represented by the metallic housing 29. Naturally, only one plug-and-jack connection is completed between any two adjacent blocks if the pads are to be connected in series. v

Block 29 is formed with three cylindrical bores 33, 34 and 35 respectively accommodating the resistors 1, 2 and 3 of the T-network, these resistors having a common terminal formed by a printed circuit 40 on an insulating cover plate 39 which is disposed in a depression 38 at the top of the block. An enlargement 60 of printed conductor 40' is capacitively coupled with the metallic housing 29 so as to form the shunt condenser similarly designated in FIG. 1.

Shunt impedance 61 is constituted by a ferrite bead on a grounded lead of resistor 3, this lead being clamped in a split sleeve 43 resiliently fitted into an extension 42 of bore 35. A lid 37 removably overlies the narrow top side of block 29 to close the space 38 against the outside.

Two pairs of chambers 44, 45 and 46, 47" are formed at symmetrical locations in the block 29, a further chamber 50 being disposed between chambers 45 and 47. Chambers 44, 46 and 50 respectively accommodate the reed relays 11, 12 and 15 whose construction has been shown in detail, for the relay 11, in FIG. 6. As seen in the latter figure, each of these relays comprises a glass tube 53, longitudinally traversed by the associated reed-type switch contacts (e.g. 8) which can be subjected to a magnetic field from the surrounding relay coil 11a. This coil is shown disposed between a pair of metallic flanges 55 which surround a nonmagnetic retaining tube 54, e.g., of brass, and which are formed with tubular flanges 56 extending outwardly through the chamber walls by way of passages 57 indicated in FIG. 4. Reeds 8 are part of a circuit 59 which is closed in the position illustrated in FIG. 4, as is its companion circuit 59' represented by the contacts of relay 12 while the circuit formed by contact 10 of relay 15 is open. The connections between the reed contacts and the terminals 31, 32 are printed circuits on insulating supporting plates 48, 49 in chambers 45 and 47, respectively, these connections being so shaped as to form the inductances 58a, 58b, 58c and 58d described with reference to FIG. 1. Chambers 45 and 47 are open toward the bored face 51 of block 29, adjoining face 52' ofblock 29', and closed toward the opposite face 52 by the plates 48, 49; the positions of the plugs and jacks is interchanged on adjoining blocks as indicated at 32, 32'.

A- cable extends out of block 29 to connect the coils of relays 11, 12 and 15 to transistor 17 and control lead 14, these elements being carried on an external mounting plate 62 which also has printed circuitry for connecting the electrodes of transistor 17 to the binding post 63 of lead 14 and posts 64 for the conductors of cable 65. The posts 64 are plug-in connections which may be easily detached. 7

It will thus be seen that we have provided a highly compact assembly for the purpose described in which all passive impedance elements such as resistors 1-3, capacitance 60 at inductances 58a etc. and 61 are well shielded in cavities of a conductive block suitably dimensioned to provide the desired wave impedance. The selector switches 2426, illustrated diagrammatically in FIG. 2, may be of conventional construction and are connected to each block only via transmission line 14.

We claim:

1. A damping network comprising a plurality of attennation pads composed of passive impedance elements; relay means for each pad having contacts connected between input and output terminals of the associated pad for directly interconnecting said terminals independently of said impedance elements; a control circuit individiual to each pad for operating said relay means thereof; a support for each pad having said impedance elements, relay means and control circuit thereof mounted thereon, the supports of the several pads being provided with coupling means for electrically interconnecting said pad; and selector means common to all said pads for individually energizing the control circuits thereof, said selector means being physically separated from said supports and being detachably connected to said control circuits.

2. A damping network as defined in claim 1 wherein said selector means comprises at least one switch with a plurality of bank contacts and a diode matrix connecting said bank contacts to said control circuits.

3. A damping network as defined in claim 2 wherein said pads are assembled in at least one group of four pads with damping factors giving, in different combinations, a set of ten decadic values of overall attenuation.

4. A damping network as defined in claim 1 wherein said relay means comprises a plurality of reed relays for each pad.

5. A damping network as defined in claim 4 wherein said supports comprise prismatic blocks juxtaposable in a stack, each support being provided with substantially cylindrical bores for accommodating said impedance elements and with separate chambers for accommodating said reed relays.

6. A damping network as defined in claim 5 wherein said impedance elements include resistors lodged in said bores.

7. A damping network as defined in claim 6 wherein said impedance elements further include inductive leads connecting said resistors to said input and output terminals.

8. A damping network as defined in claim 6 wherein a lead connected to one of said resistors.

9. A damping network as defined in claim 6 wherein said blocks are metallic and said impedance elements further include a conductor interconnecting said resistors, said conductor having an enlarged portion capacity coupled with the respective block.

10. A damping network as defined in claim 5 wherein said control circuit includes a transistor mounted externally on the respective block, said reed relays including a first and a second relay shunted across said transistor for closing two pairs of contacts, connected in series with said pad, and a third relay in series with said transistor for opening a further pair of contacts, connected across the series combination of said pad and said two pairs of contacts, in a nonconductive state of said transistor.

References Cited UNITED STATES PATENTS 1,800,305 4/1931 Lindsay 323- X 1,880,800 10/1932 Chestnut et al 333-81 X 2,010,644 8/1935 Rienstra 333-81 X 2,246,293 6/1941 Collard 333-81 2,261,961 11/1941 Christensen et al. 323-79 2,823,358 2/1958 Means et al. 3,014,187 12/1961 Sher et a1. 333-81 3,208,016 9/1965 Kraus 333-81 FOREIGN PATENTS 488,565 7/ 1938 Great Britain. 628,737 9/ 1949 Great Britain.

KERMAN K. SAALBACH, Primary Examiner W. H. PUNTER, Assistant Examiners US. Cl. X.R.

gg 3 UNITED STATES PATENT OFFICE 1 CERTIFICATE OF CORRECTION Patent No. 3 474.356 Dated 26 March 1971 Inventofls) Wolfgang HOFFMANN et 31.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, line 6, change "Wandel uber,Golterman to Wandel u. Goltemann Signed and sealed this 13th day of July 1971.

(SEAL) Attest:

EDWARD M.FLETCHER J'R. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

1. A DAMPING NETWORK COMPRISING A PLURALITY OF ATTENUATION PADS COMPOSED OF PASSIVE IMPEDANCE ELEMENTS; RELAY MEANS FOR EACH PAD HAVING CONTACTS CONNECTED BETWEEN INPUT AND OUTPUT TERMINALS OF THE ASSOCIATED PAD FOR DIRECTLY INTERCONNECTING SAID TERMINALS INDEPENDENTLY OF SAID IMPEDANCE ELEMENTS; A CONTROL CIRCUIT INDIVIDUAL TO EACH PAD FOR OPERATING SAID RELAY MEANS THEREOF; A SUPPORT FOR EACH PAD HAVING SAID IMPEDANCE ELEMENTS, RELAY MEANS AND CONTROL CIRCUIT THEREOF MOUNTED THEREON, THE SUPPORTS OF THE SEVERAL PADS BEING PROVIDED WITH COU- 